fixed bug where overwrite warning on recipe save didn't work properly

new shaders:

• brightness (rough inverse of dramatic)
• contrast (inverse of invert x2)
• toon
• halftone
• gaussian (better looking than vanillas "blur")

new layer effects:

• channel_cycle_additive
• channel_cycle_exclusive

these are both different implementations of the same idea of "what if each shader on the stack was applied to different RGB channels" so shader 1 is on the red channel, 2 on green channel, 3 on the blue channel, then 4 is back on red

channel_cycle_exclusive is generally a little more intuitive with what you end up seeing, ..._additive is more chaotic but can look very cool -- both are generally unreasonably powerful even for relatively small stack sizes